Add tests

[MeikeWeiss]

See Issue #338

[codecov]

Codecov Report

❌ Patch coverage is 98.98990% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 73.31%. Comparing base (3524247) to head (50c5130).

Files with missing lines	Patch %	Lines
unit_tests/Test_Graphs.g	98.18%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #339      +/-   ##
==========================================
+ Coverage   70.58%   73.31%   +2.72%     
==========================================
  Files          62       63       +1     
  Lines       17269    17368      +99     
==========================================
+ Hits        12190    12734     +544     
+ Misses       5079     4634     -445     

Files with missing lines	Coverage Δ
gap/PolygonalComplexes/graphs.gd	100.00% <ø> (ø)
unit_tests/Test_BorderCases_PolygonalComplex.g	100.00% <100.00%> (ø)
unit_tests/Test_Generating_Families.g	100.00% <100.00%> (ø)
unit_tests/Test_Inferences_PolygonalComplex.g	100.00% <100.00%> (ø)
unit_tests/test_main.g	98.30% <100.00%> (+0.15%)	⬆️
unit_tests/Test_Graphs.g	99.54% <98.18%> (-0.46%)	⬇️

... and 5 files with indirect coverage changes

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